Photoconductography employing cobaltous or nickelous hydroxide



Oct. 9, 1962 R. F. REITHEL 3,

PHOTOCONDUCTOGRAPHY EMPLOYING COBALTOUS OR NICKELOUS HYDROXIDE Filed June 27, 1961 ALKALINE ox/o/zm/e i COBAUUUS AGENT E 20 HYDROX/DE 53%5/5 ,5 I 23 /5 y y A I /5 I I? /6 l6 RAYMOND E RE/THEL INVENTOR.

BY XMM WM 72 ATTORNEYS tates This is a continuation-in-part of U5. Serial No. 45,947, filed July 28, 1960, and now abandoned.

This invention relates to photoconductography.

Photoconductography forms a complete image at one time or at least a non-uniform part of an image as distinguished from facsimile which at any one time produces only a uniform dot. The present invention would be useful with facsimile but finds its greatest utility in photoconductography.

Cross reference is made to the following series of applications filed July 28, 1960, concurrently with the application of which this is a continuation-in-part.

Serial No. 45,940, John W. Castle, Jr., Photoconductography Employing Reducing Agents.

Serial No. 45,941, Raymond F. Reithel, Photoconductolithography Employing Nickel Salts, and continuationin-part Serial No. 120,863, filed June 7, 1961.

Serial No. 45,942, Raymond F. Reithel, Photoconductolithography Employing Magnesium Salts.

Serial No. 45,943, Raymond F. Reithel, Photoconductography Employing Spongy Hydroxide Images, now abandoned, and continuation-impart Serial No. 120,035, filed June 27, 1961.

Serial No. 45,944, Raymond F. Reithel, Method for Making Transfer Prints Using a Photoconductographic Process.

Serial No. 45,945, Raymond F. Reithel, Photoconductography Employing Manganese Compounds.

Serial No. 45,946, Raymond F. Reithel, Photoconductography Employing Molybdenum or Ferrous Oxide, now abandoned, and continuation-in-part Serial No. 120,- 036, filed June 27, 1961.

Serial No. 45,948, Donald R. Eastman, Electrophotolithography.

Serial No. 45,949, Donald R. Eastman, Photoconductolithography Employing Hydrophobic Images.

Serial No. 45,950, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Electrolytic Images to Harden or Soften Films.

Serial No. 45,951, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Absorbed Metal Ions, now abandoned, and continuation-in-part Serial No. 120,038.

Serial No. 45,952, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Spongy Images Containing Gelatin Hardeners.

Serial No. 45,953, John I. Sagura, Photoconductography Employing Alkaline Dye Formation.

Serial No. 45,954, John J. Sagura and James A. Van- Allan, Photoconductography Employing Quaternary Salts.

Serial No. 45,955, Franz Urbach and Nelson R. Nail, Uniform Photoconductographic Recording on Flexible Sheets.

Serial No. 45,956, Franz Urbach and Nelson R. Nail, High Contrast Photoconductographic Recording.

Serial No. 45,957, Nicholas L. Weeks, Photoconductography Involving Transfer of Gelatin.

Serial No. 45,958, Donald R. Eastman, Photoconductolithography Employing Rubeanates.

Serial No. 45,959, Donald R. Eastman and Raymond Unite atent C) ice F. Reithel, Electrolytic Recording With Organic Polymers.

Serial No. 46,034, Franz Urbach and Donald Pearlman, Electrolytic Recording.

Electrolytic facsimile systems are well known. Electrolytic photoconductography is also known and is described in detail in British 188,030, Von Bronk, and British 464,112, Goldmann, modifications being described in British 789,309, Berchtold, and Belgium 561,403, Johnson et al.

One form of this invention relates particularly to that group of photoconductographic processes in which the image is produced in two steps. The electrolytic image which is first deposited is only faintly visible, but it is converted, either in situ or after transfer, to a highly dense, substantially neutral image.

The other form of the invention relates particularly to a single solution electrolyte-developer for photoconductography. The single solution form employs cobalt ions with manganese and silver ions whereas the 2-step form of the invention employs either cobalt or nickel salts and one of the incidental objects of this 2-step form of the invention is to eliminate the need for silver salts which are relatively expensive.

A primary object of both forms of the invention is to produce a photoconductographic image or print which is stable to light and to mild chemical treatments such as treatment with a bleach, or the elfect of grease. Such images are particularly resistant to finger-printing. Another object of the invention is to produce a photoconductographic print which has a higher reflective density than that obtainable by direct methods, i.e. those in which a metal is deposited directly.

It is known that when nickelous hydroxide, Ni(OH) or cobaltous hydroxide, Co(OH) is treated with an alkaline oxidizing agent such as potassium persulfate at a pH greater than 8, the corresponding nickelic hydrooxide, Ni(OH) or cobaltic hydroxide, Co(OH) is produced which is quite black. The 2-step form of the present invention consists in applying this reaction as a second step in photoconductography by depositing electrolytically from an electrolyte containing cobaltous ions or nickelous ions, the cobaltous hydroxide or nickelous hydroxide. The term hydroxide is here used to cover hydrated oxides as well as simple hydroxides. The lower valence hydroxide is then converted to the higher valence hydroxide of the same metal by treating the image with an oxidizing agent such as persulfate or bromine water at relatively high pH, the latter being achieved by adding alkali. The cobaltous and nickelous ions may be provided by any water soluble salt containing these ions in the lower valence state.

The single solution electrolyte form of the invention makes use of the phenomenon that during electrolysis at certain current differences, there is a large increase in pH at the photoconductor and at the electrolyte interface.

This increase in pH is utilized to produce the precipitation of the black absorption complex formed between manganese dioxide, cobalt dioxide and reduced silver from a solution containing manganese, cobalt and silver ions, simultaneously with the electrolytic development. At low current densities, produced at the less exposed areas of the photoconductor, only silver will be deposited with no formation of the complex. This is proper for highlights. As the current density is increased, namely in areas of increased exposure, a point is reached where the black adsorption complex formation begins and at any current density above this, the black complex will be produced in increasing amounts. In this way an increase in both density and contrast is eifected. The manganous and silver ion alone will form the complex as described in 2-step processes in my co-filed application entitled Photoconductography Employing Manganese Compounds. However, such a system does not work for single solution photoconductography, apparently because such a simple complex, if formed during the electrolysis does not adhere well to the photoconductor surface. The addition of cobalt gives several advantages. It aids in the adhesion of the deposited material which is its primary function in this case. It adds to the black complex which is formed in an alkaline medium. It increases the stability of the image material to finger-printing and, when it is desirable to bleach the sensitizing dye from the photoconductor, the cobalt increases the stability of the image to the action of mild chemical bleaches used. The cobalt furthermore limits the deposition of silver at low current densities and thus produces a mild toe-cutting effect when compared to images produced by a silver ion alone or the silver-manganese complex.

Certain prior systems involve the deposition of metallic sulfide by reduction at the cathode, whereas the present invention (not involving sulfide) actually involves two processes simultaneously with image formation, namely the electrolytic reduction and the formation of the complex material by means of the pH shift at the cathode. The sulfide systems give lower contrast and lower maximum density.

Thus one purpose of this single solution form of the invention is to provide a single step process producing images of higher neutral density than that achieved by silver ion or silver complex developers.

An incidental advantage of the invention is that it provides a developer solution which is stable over long periods of time if stored in closed bottles.

The invention will be more fully understood from the following description when read in connection with the attached drawing which shows a schematic flow chart of a preferred embodiment of the invention.

In the drawing a transparency illuminated by a lamp 11 is imaged by a lens 12 on a zinc oxide in resin layer 15 carried on a conducting support 16. The transparency 10, is moved continuously to the left as indicated by the arrow 17 and the photoconductive zinc oxide layer 15 is moved to the right synchronously with the image of the transparency, as indicated by the arrow 18.

Immediately following exposure, while the photoconductive image persists, the exposed sheet is passed through the electrolytic bath applied by a brush 20; the potential difference is supplied between the brush 20 and a roller 21 from a source being indicated schematically at 22. The electrolyte in the brush 20 contains cobaltous salt and hence cobaltous ions which, due to the passage of direct current in the exposed areas of the layer 15, deposits cobaltous hydroxide to form an image 23.

As in all photoconductography using zinc oxide as the photoconductor, alternating current may be applied since the zinc oxide electrolyte interface acts as a rectifier making the zinc oxide the cathode.

Parts of this image material may be transferred to a receiving sheet (some of the cofiled applications listed above discuss the advantage of transferred image material), or in the example shown is treated directly by a second brush 26 containing an alkaline oxidizing agent. This oxidizes the cobaltous hydroxide image 23 to a black cobaltic hydroxide image 27. In this case the image 27 constitutes the final print.

Nickelous hydroxide can be similarly converted to nickelic hydroxide and is hence useable in this same process.

In the single developer form of the invention, the brush 20 contains cobalt, manganese and silver ions and the image deposited thereby is the final image (without the second swabbing) which image consists of metallic silver in the highlights and increasing amounts of cobalt-manganese-silver complex, primarily oxides and reduced silver, at increasing densities.

As examples of the present invention, the following gave excellent high density prints.

Example 1 A dye-sensitized zinc oxide in resin layer on a conducting support was exposed imagewise through a 0.3 density increment step-wedge to 400 ft. candle tungsten illumination for 5 seconds. The conducting image was developed electrolytically, using a viscous sponge brush electrode (such as 20) held at 70 volts potential positive with respect to the zinc oxide layer, and containing a solution of 1% nickelous chloride hexahydrate. Development was carried out by brushing across the surface of the zinc oxide photoconductor and the resulting faintly visible nickelous hydroxide image was dried with an absorbent tissue. This image was intensified, chemically, by bathing it with a 4% solution of potassium persulfate with a pH between 9 and 10 achieved by adding sodium hydroxide. A black image of higher valence nickelic hydroxide in the form of and relative to the amount of the electro-deposited nickelous hydroxide resulted. This print was then bathed in a solution consisting of 2% maleic acid in acetone to remove the sensitizing dye from the non-image areas of the print. The nickel hydroxide image is resistant to such bleach.

Example 2 A dyesensitized zinc oxide layer on a conducting support was exposed imagewise through a 0.3 density increment step-wedge to 400 ft. candle tungsten illumination for 5 seconds. The conducting image was then developed electrolytically, using a viscose sponge brush electrode, held at 70 volts potential positive with respect to the zinc oxide layer, and a solution of 0.75 cobaltous sulfate heptahydrate plus 0.25% manganous nitrate. Development was carried out by brushing across the surface of the Zinc oxide photoconductive layer and the resulting faintly blue cobaltous hydroxide (in manganous hydroxide carrier) was dried with an absorbent tissue. This image was intensified chemically, by bathing it with a 2% solution of potassium persulfate at a pH of 13.0 achieved by adding sodium hydroxide. A brownishblack image consisting of a higher valence cobalt oxide and/or hydrated oxide resulted in the form of and relative to the amount of the electrodeposited cobaltous hydroxide material.

Example 3 This is an example of the single solution embodiment of the invention in which the electrolyte contains cobaltous, manganous and silver ions. A dye-sensitized zinc oxide layer was exposed for 5 seconds to 400 ft. candle tungsten illumination through an 0.3 density increment step wedge. The resulting conducting image was then developed, electrolytically, using a solution of 0.75% cobaltous sulfate heptahydrate plus 0.25% manganous nitrate plus 0.35% silver nitrate contained in a viscose sponge brush electrode held at 70 volts potential positive with respect to the zinc oxide layer and using three slow strokes development (1 inch per second). A density of 0.90 was obtained for the 2000 ft. candle second exposure with a gamma of 0.87.

To compare this example with the prior silver sulfide systems, a similarly exposed zinc oxide layer Was developed as above by brushing with a solution of 1% silver nitrate in 2% thiourea. The maximum density in this case Was only 0.50 and the gamma was only 0.30. Thus the present invention gives much more satisfactory density and contrast. In this Example 3 (and in Examples 4 and 5 below) the ions can be supplied in any form, using any soluble salt of the material involved. For example cobaltous nitrate, cobaltous acetate, manganous sulfate, manganous acetate, silver acetate and silver sulfate can all be substituted interchangeably for the corresponding salts in the above formula. The concentration of the developer is. not too critical. Those given are more or less optimum but can be varied over a wide range. For example cobalt salt concentrations between .05% and saturation may be used. The ratios of concentrations of the various components are more critical. For instance, it is desirable to have the manganese salt concentrations between /1 and 1 times the cobalt salt concentration and a to have the silver salt concentration between and 1 times the cobalt salt concentration. This developer works equally well with the forms of photoconductography involving simultaneous exposure and development. It is illustrated in the accompanying drawing as used with subsequent development of the exposed zinc oxide layer.

Example 4 A dye-sensitized zinc oxide in resin layer was exposed for 5 seconds to 50 ft. candle tungsten illumination through a 0.3 density increment step-wedge. The resulting conducting image was then developed electrolytically, using a solution of 0.75% cobaltous sulfate heptahydrate plus 0.25% manganous nitrate plus 0.5% silver lactate contained in a viscose sponge brush electrode held at 70 volts potential, positive with respect to the zinc oxide layer and using two slow strokes development at 1 inch per second. An image consisting of manganese dioxide-cobalt dioxide and reduced silver formed on the photoconductor surface.

Example 5 A photoconductographic print was made as in Example 3. This print was then bathed in a solution of 2% maleic acid in acetone for seconds. The dyes were thus bleached from the zinc oxide layer and the image material was unaifected by the bleach. This was confirmed by comparison with the print made in the first example. This contrast is improved compared to the print of Example 3 since the highlights are of a lighter tone.

The fact that this single solution electrolytic development operates more slowly than the simple silver or silver complex systems, does not involve any difficulty since the ditferenceof rate is not very great. Somewhat slower development stroke are used for hand processing and presumably for machine development, the machine should be run at slightly slower speeds, but the present invention has been found to work with standard rates of development.

In the electrolytic processes described in this and the various copending applications referred to above there are in general no critical or special limits on the potential applied or the concentration of the salts in the electrolyte. Of course the potential cannot be so high that it causes electrical breakdown of the photoconductive layer and cannot be so low that there is no appreciable electrolytic effect Within a reasonable time. Similarly the concentration of the salt in the electrolyte cannot be above saturation or cannot be so low that there is no appreciable deposit during a reasonable period of electrolytic action.

However, in the case of nickel salts when the hydroxide of the metal is to be deposited, there is a minimum voltage (about 30 volts) and a maximum concentration (about 3%), since at lower voltage or at higher concentrations the metal itself, without a useful amount of the hydroxide, tends to deposit. All of the examples involving nickel given in the present series of applications do 6 have concentrations below 3% and voltages above 30 v. so that useful amounts of hydroxide are deposited. Whether metal is also deposited is of little concern.

Nickel hydroxide is much more hydrophilic than nickel metal and is more absorbent (spongy) than nickel itself. AlSo nickel metal images do not have satisfactory optical density whereas the deposit of nickelous hydroxide and conversion to nickelic oxide does give a high density. These various eflfects are involved in difierent applications of this present series. Also any concentration-above 3% not only gives adverse eifects, but adds to the cost of whichever process is involved.

As with other materials, the upper limit on the voltage is that imposed by electrical breakdown and the lower limit on concentration of nickel salts is merely that amount which gives an appreciable deposit in a reasonable time under the voltage available. This lower limit is obviously not critical.

Cobalt and iron salts behave somewhat like the nickel salts. At higher concentrations and lower voltages, the ratio of metal (or at least of a metallic like deposit which appears) to hydroxide increases. Cobalt hydroxide images appear light blue and ferrous hydroxide images appear olive green. When the process involves producing cobaltic oxide (which has a good density compared to cobalt metal images) the concentration should be below 3% and the voltage above 30 v. (as in the case of nickel). Iron is not used in such processes since ferric oxide and hydroxide are light colored. When the process involves sponginess or physical absorption by the image, both iron and cobalt must again be used in concentrations below 3% and at voltages above 30 v. since the hydroxide images are much more absorptive than the metal images. When the process involves the hydrophilicity of the image, 30 v. is still the lower useful limit and the preferred concentrations are still below 3% although higher concentrations of iron salts and particularly of cobalt salts still give useful results because the metal images themselves have considerable hydrophilicity although not nearly as good as that of the corresponding hydroxides. Finally, when the process involves reduction (nickel hydroxide images by themselves are never used in reducing processes) the limits on concentration and voltages are only the general ones (i.e. up to saturation and between the voltage which gives an appreciable deposit in a reasonable time and the voltages which cause breakdown) because the metal image itself is reducing for bolt cobalt and iron.

Having given various examples of the invention and preferred arrangements thereof, it is pointed out that the invention is not limited to these specific examples but is of the scope of the appended claims.

I claim:

1. In a photoconductographic process in which an image pattern of variations in electrical conductivity is produced in a photoconductive layer, the steps comprising placing the layer in electrical contact with an electrolyte containing lower of plural valency state ions selected from the group consisting of nickelous and cobaltous, passing direct current through the layer and electrolyte distributed in accordance with said pattern to deposit a hydroxide of said ions and treating the deposit with an alkaline solution of an oxidizing agent to convert it to the corresponding higher valence hydroxide.

2. In a photoconductographic process the steps of electrolytically depositing an image of hydroxide selected from the group consisting of nickelous hydroxide and cobaltous hydroxide and treating said image with an alkaline oxidizing agent to form the corresponding higher valence hydroxide.

3. The process according to claim 2 in which nickelous hydroxide is deposited from an electrolyte containing nickelous chloride.

4. The process according to claim 2 in which cobaltous hydroxide is deposited from an electrolyte containing cobaltous sulfate.

5. The process according to claim 2 in which the alkaline oxidizing agent is a solution of potassium persulfate brought to a pH greater than 8 by the addition of an alkali.

6. In a photoconductographic process in which an image pattern of variations in electrical conductivity is 3,057,788 7 8 produced in a photoconductive layer, the steps compris- References Cited in the file of this patent ing placing the layer in electrical contact with an elec- UNITED STATES PATENTS trolyte containing manganese, cobalt and silver ions,

passing direct current through the layer and electrolyte 571,532 Langhans 1896 distributed in accordance with said pattern to deposit a 5 737,882 Strecker P 1903 manganese hydroxide-cobalt hydroxide-silver adsorption 3,010,883 Johnson et 1961 complex.

:UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,057,788 Oct0ber 9, 1962 Raymond F. Reithel It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, line 1, and, in the heading to the printed specification, line 4, name of inventor, for

"Raymond F. Riethel", each occurrence, read Raymond F, Reithel column 5, line 43, for "stroke?! read strokes column 6, line 39 for "bolt" read 100th Signed and sealed this 9th day of April 19630 (SEAL) Attest:

ESTON G. JOHNSON DAVID L. LADD Attesting Officer I Commissioner of Patents i 

1. IN A PHOTOCONDUCTOGRAPHIC PROCESS IN WHICH AN IMAGE PATTERN OF VARIATIONS IN ELECTRICAL CONDUCTIVITY IS PRODUCED IN A PHOTOCONDUCTIVE LAYER, THE STEPS COMPRISING PLACING THE LAYER IN ELECTRICAL CONTACT WITH AN ELECTROLYTE CONTAINING LOWER OF PLURAL VALENCY STATE IONS SELECTED FROM THE GROUP CONSISTING OF NICKELOUS AND COBALTOUS, PASSING DIRECT CURRENT THROUGH THE LAYER AND ELECTROLYTE DISTRIBUTED IN ACCORDANCE WITH SAID PATTERN TO DEPOSIT A HYDROXIDE OF SAID IONS AND TREATING THE DEPOSIT WITH AN ALKALINE SOLUTION OF AN OXIDIZING AGENT TO CONVERT IT TO THE CORRESPONDING HIGHER VALENCE HYDROXIDE. 